Increasing importance is being attached to the provision of pressurized gas for the sudden filling of an area with a previously lower pressure, e.g. ambient pressure in restraining systems is used in motor vehicles, so-called air bags. For this purpose essentially three systems are known up to now. In one case the filling gas is produced by a chemical reaction as needed. However, this presupposes the existence of substances which are able to produce large quantities at the time of their reaction, but in the initial state only have a limited space requirement. For this purpose use can be made of solid propellants, but only those which exclusively or preponderantly produce inert gas, so as not to expose the vehicle occupants to toxic risks. In practice use has mainly been made up to now of sodium azide (N.sub.2 production) (DE-A-2,236,175). As a result of the high reaction temperature of about 1500.degree. C. particular heat protection measures are needed on the restraining system, e.g. the bag material. In addition, the bag material must be able to hold back unburned particles of the propellant. Propellant residues left behind after the release are highly toxic. When used in motor vehicles the toxicity of sodium azide constitutes a latent risk to the environment and requires special measures when the vehicles are disposed of.
In place of sodium azide nitrocellulose-based propellants have also been proposed, but in the case thereof higher gas temperatures must be controlled and there is in particular a high proportion of toxic CO, which can lead to flammable mixtures when hydrogen is present. In addition, NC does not have a satisfactory thermal stability.
These disadvantages also apply to numerous other propellants which have been tested.
In addition, hybrid systems are known (WO 91/11347), in which, besides a stored, inert pressurized gas, use is made of a gas-producing propellant. The propellant is ignited on release and the gas produced by the chemical reaction is transferred together with the inert gas into the restraining system. Once again the aforementioned disadvantages occur, although to a lesser extent.
In the third system use is exclusively made of stored, non-toxic pressurized gas, which is transferred from the pressurized gas storage vessel into the restraining system. These systems admittedly have a relatively large space requirement, but are preferable from the safety and environmental standpoints. Such a system requires an opening mechanism on the pressure container acting in milliseconds and for this purpose the container is provided with a bursting closure. Since during the flow from the pressurized gas container into the restraining system the gas is cooled due to the Joule-Thomson effect and icing can occur, corresponding heat must be supplied through the opening mechanism.
The problem of the present invention is to propose a pyrotechnic charge which, in the case of a minimum space requirement, permits a release of the gas stored in the container by destroying the bursting disk within milliseconds and which also compensates the Joule-Thomson effect.